In the past, information systems used to be defined primarily by their functionality: data and functions were kept separate and linked together by means of input and output relations.
The object-oriented approach, however, focuses on objects that represent abstract or concrete things of the real world. These objects are first defined by their character and their properties which are represented by their internal structure and their attributes (data). The behaviour of these objects is described by methods (functionality).
Objects form a capsule which combines the character to the respective behaviour. Objects should enable programmers to map a real problem and its proposed software solution on a one-to-one basis.
Typical objects in a business environment are, for example, ‘Customer’, ‘Order’, or ‘Invoice’. From Release 3.1 onwards, the Business Object Repository (BOR) of SAP Web Applicaton Server ABAP has contained examples of such objects. The BOR object model will be integrated into ABAP Objects in the next Release by migrating the BOR object types to the ABAP class library.
A comprehensive introduction to object orientation as a whole would go far beyond the limits of this introduction to ABAP Objects. This documentation introduces a selection of terms that are used universally in object orientation and also occur in ABAP Objects. In subsequent sections, it goes on to discuss in more detail how these terms are used in ABAP Objects. The end of this section contains a list of further reading, with a selection of titles about object orientation.
Objects are instances of classes. They contain data and provides services. The data forms the attributes of the object. The services are known as methods (also known as operations or functions). Typically, methods operate on private data (the attributes, or state of the object), which is only visible to the methods of the object. Thus the attributes of an object cannot be changed directly by the user, but only by the methods of the object. This guarantees the internal consistency of the object.
Classes describe objects. From a technical point of view, objects are runtime instances of a class. In theory, you can create any number of objects based on a single class. Each instance (object) of a class has a unique identity and its own set of values for its attributes.
In a program, you identify and address objects using unique object references. Object references allow you to access the attributes and methods of an object.
In object-oriented programming, objects usually have the following properties:
Objects restrict the visibility of their resources (attributes and methods) to other users. Every object has an interface, which determines how other objects can interact with it. The implementation of the object is encapsulated, that is, invisible outside the object itself.
You can use an existing class to derive a new class. Derived classes inherit the data and methods of the superclass. However, they can overwrite existing methods, and also add new ones.
Identical (identically-named) methods behave differently in different classes. In ABAP Objects, polymorphism is implemented by redefining methods during inheritance and by using constructs called interfaces.
Uses of Object Orientation
Below are some of the advantages of object-oriented programming:
· Complex software systems become easier to understand, since object-oriented structuring provides a closer representation of reality than other programming techniques.
· In a well-designed object-oriented system, it should be possible to implement changes at class level, without having to make alterations at other points in the system. This reduces the overall amount of maintenance required.
· Through polymorphism and inheritance, object-oriented programming allows you to reuse individual components.
· In an object-oriented system, the amount of work involved in revising and maintaining the system is reduced, since many problems can be detected and corrected in the design phase.
Achieving these goals requires:
· Object-oriented programming languages
Object-oriented programming techniques do not necessarily depend on object-oriented programming languages. However, the efficiency of object-oriented programming depends directly on how object-oriented language techniques are implemented in the system kernel.
· Object-oriented tools
Object-oriented tools allow you to create object-oriented programs in object-oriented languages. They allow you to model and store development objects and the relationships between them.
· Object-oriented modeling
The object-orientation modeling of a software system is the most important, most time-consuming, and most difficult requirement for attaining the above goals. Object-oriented design involves more than just object-oriented programming, and provides logical advantages that are independent of the actual implementation.